


Kryptonian biology and the scientific method

by queersintherain



Category: Supergirl (TV 2015)
Genre: (Alex and Kara communicate a lot), Alien Biology, Alien/Human Relationships, Blow Jobs, F/F, Fuck Or Die, Fuck Or Unpleasant Consequences, Knotting, Non-Human Genitalia, Oral Sex, Sort Of, brief Alex Danvers/OMC, minor dubcon for teenage sex (Alex/OMC) without good communication, of a sort
Language: English
Status: Completed
Published: 2020-01-14
Updated: 2020-01-14
Packaged: 2021-02-25 07:15:16
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 15,125
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22252207
Author URL: https://archiveofourown.org/users/queersintherain/pseuds/queersintherain
Summary: “Are you sure they don't have sex, or is that just what they told you to keep you all repressed?”“No, I said they don’t,” Kara snaps back, finally, and it feels good, getting Kara to lose her cool and finallyengagein the argument they’re having. “The Codex fits everyone with a subdermal implant that prevents sexual arousal. It keeps us from distraction.”Alex, in the middle of digging her heels in to really get going again, comes up short. The Codexwhat?--Teen human and teen Kryptonian are both curious about sex and make some questionable decisions. (It works out).
Relationships: Alex Danvers/Kara Danvers
Comments: 27
Kudos: 431





	Kryptonian biology and the scientific method

**Author's Note:**

  * For [outlier](https://archiveofourown.org/users/outlier/gifts).



> This was supposed to be for this year's Secret Kalex Santa, but it just KEPT GROWING, and I could not get it finished in time. So, here it is now! Merry belated Kalexmas outlier, I hope you like it! 
> 
> The arral is borrowed (with permission, and a couple of modifications) from Alsike--thank you! 
> 
> And thank you as always to the friends who helped me with this--you are all wonderful, and I really appreciate your time and your thoughts!

Lately, Alex has been thinking about sex. As a scientist, she knows that’s one of the things that happens to most people at puberty. Your hormone levels increase, your body starts to sexually mature, and because it’s ready for reproduction, it starts wanting to get started with that.

Thinking about sex is typical for people her age, Alex knows. Praxis is too, by the numbers.

Praxis has been an issue. Or rather, having an alien roommate with super hearing has been an issue, because the thought of doing anything while Kara might hear her is mortifying. The few times Alex has gotten the opportunity though, when Kara has been out at something or other, she’s flopped down on her stomach on her bed and wriggled her hands between her legs. It took a little while to figure out, pushing and stroking and fumbling around trying to stick a finger inside herself, but eventually her underwear were soaked and she was shaking with pleasure.

Thoughts - check.

Initial attempts at masturbation - check.

Sex with another person seemed like the next logical step.

Jason Kelly had seemed like a good candidate to try things with when Alex had been talking to him at school. He was nice enough to look at and hadn’t been mean to Kara, when Kara had first arrived on Earth.

Right now though, with his dick in her mouth, Alex isn’t so sure she wants to do this after all. They’d been kissing, and that was nice, and then he’d run his hand up her side, brushing over her breast, and all of a sudden she’d felt heavy and slick down there, the feeling more exciting, _intense_ than usual because she was with another person. Even better, they were at Jason’s house, up in his room because his parents were out at a work meeting, and Kara was still at school at science club, so there was no chance of her accidentally hearing something through the walls.

When Jason, hard against her thigh (which was scary, but sort of thrilling too, that this was because of her), asked her if she would put her mouth on him, it seemed like a good idea, a new thing to experiment with. And then things got significantly less exciting, and Alex has gotten less sure that sex is actually something she’s into.

Her knees hurt from kneeling on the floor beside his bed, and her jaw is sort of sore from keeping her mouth open for so long, nevermind the dryness from using all of her saliva sucking for... minutes now, and it’s a little smelly, honestly. Jason is enjoying himself, groaning and straining his hips, and Alex hopes he’ll come soon so she can make an excuse and go home, because she has a chem test to study for. She thinks she’s done with this experiment.

“Alex?” Kara asks, and Alex jerks back, suddenly horrified—Jason’s dick comes out of her mouth with a terrible wet sucking sound. He groans, and cum spurts out of it in ropes, hot all over Alex’s face and shirt. Alex’s shock ( _he was supposed to tell her when he was going to come_ ) and disgust are drowned out by the panicked hammering of her heart. Kara can’t be here. There’s no way Kara is here.

But when she turns, Kara is in the door of the room, hair damp from the rain, clutching her backpack so tight she’s probably ripped it, staring at Alex.

“What are you doing here?” Alex snaps. “Go home!”

Kara opens her mouth to say something and then closes it again, and—she’s gone. Alex feels like she’s going to melt into the floor. This can’t be happening. Kara can’t have been just _here_ , watching Alex giving a _blowjob_.

And Jason is _laughing_ , tucking his penis back into his underwear where he’d pulled it from when Alex had first settled on the floor. “Your sister really does follow you everywhere, doesn’t she?”

Alex is hot with humiliation, burning with it, because she has no excuse, no explanation she can offer for Kara’s presence while protecting her secret. _Sorry Kara turned up, she was probably using her alien super hearing to listen for me, or her x-ray vision to find me, I promise I didn’t tell her your address, or that I was going to be here, or what I was going to be doing._ And there’s white fluid dripping down her face—she’d told him not to come in her mouth but this is _worse_ , and Alex just wants to curl up into a ball on her bed and pretend this day never happened.

*

Of course when Alex gets home Kara is in their room, sitting on the bed and staring at the door like she’s waiting for Alex, because where else would she go? Ever since Kara came Alex’s life has been Kara’s, and there’s nowhere she can go to get a little peace when she wants to hide. Nowhere, nothing that’s hers left. Making out with Jason had felt _good_ , and then Kara had shown up, and now all Alex has is a damp, uncomfortable t-shirt under her hoodie and the burning urge to yell at someone.

“Why were you following me?” Alex snaps, throwing her backpack down on her bed and turning back to glare. Kara’s standing now, eyes wide and a little wet, twisting her hands in the hem of her t-shirt for that ‘science achievers’ summer camp Eliza and Jeremiah sent them to last year.

“I thought I heard you choking,” Kara says. “What were you doing? Why did you have your mouth on his penis?”

Alex makes an inarticulate noise in the back of her throat. There is no fucking way. Kara cannot have been on Earth for this long without figuring out what oral sex is. “I was giving him a blowjob,” she says, hoping her scowl will make up for how red her face is. “I know you know what a blowjob is.” Alex isn’t explaining it. Kara can google it, Alex knows she knows how to do that.

Kara makes a frustrated noise, letting go of her shirt. “I know what it is, but I don’t know why you were doing it.”

“Because it felt good,” Alex snaps, even though it really didn’t. It smelled like sweat and gross boy musk, and she needs to have a shower. She had been choking a little, but it was fine, it was normal, Vicky told her, and none of that meant Kara should have been listening.

“How could it feel good?” Kara asks, incredulous. “You were only stimulating his sex organ, weren’t you? He wasn’t touching yours?”

For the most part, Kara has adapted to Earth in the years since she came here. She picked up English easily, and even though slang took longer, she definitely has it down, and Alex thinks it’s just her luck that Kara would choose now to talk like a fucking alien again.

“I was giving him a blowjob because I wanted to,” she says. “You need to stop listening to me all the time Kara. What if you were with your boyfriend and I was listening at the door?” Not that Jason is her boyfriend. She’s probably never going to see him again after the way she ran out of his house.

“I wouldn’t,” Kara says, stilling.

“Because you don’t have a boyfriend, or any boy who wants to do it with you,” Alex snaps, feeling the poison of her words as they’re coming out of her mouth, half-hating herself for saying them. But hurling them at Kara is the only thing that feels like it can cover the sharp twist in her stomach. Kara _saw her._

“Because we don’t do that,” Kara says, jaw tense, that cold alien look she had when she dropped into Alex’s life sliding over her like a mask. “Copulation is beneath the dignity of the high houses.”

Of course it is. And Kara saw Alex on her knees sucking dick—just another low, dirty human. One more way that Alex is beneath her, that she’ll never measure up, never be worthy of the girl who can touch the stars.

“Oh, the high houses, right,” Alex says. “I forgot about your super special Kryptonian dignity.”

“I do have dignity, unlike you,” Kara says, and Alex sees red.

“Every species that can have sex does, Kara,” Alex says. “Humans do it to relieve tension, and to continue the species... to communicate love and desire for one another, and because it feels pleasurable. ‘Copulation’ might not be dignified, but it fulfills an important role in society, and even if you all had babies through the Codex, I’m pretty sure whoever told you the high houses didn’t have sex was full of shit.” Even if Alex doesn’t feel all of these things right now, even if all she can feel aside from the anger is the humiliation of being caught, it doesn’t mean she doesn’t believe them, and she can’t listen to Kara thinking she’s dirty for wanting to have sex, because it’s something she’s desperately trying not to believe herself. Having wanted to have sex, whatever, because she’s still not sure if she wants to try again now. It would probably feel better if it were the kind of sex that involved someone touching her, at least.

“They don’t,” Kara says, face still blank.

“Are you sure, or is that just what they told you to keep you all repressed?”

“No, I said they don’t,” Kara snaps back, finally, and it feels good, getting Kara to lose her cool and finally _engage_ in the argument they’re having. “The Codex fits everyone with a subdermal implant that prevents sexual arousal. It keeps us from distraction.”

Alex, in the middle of digging her heels in to really get going again, comes up short. The Codex _what_?

She stares at Kara. “You can’t get sexually aroused? Like, even if you wanted to? You just have this thing that makes your body have no interest in sex?”

‘We don’t do that’ and ‘prevents sexual arousal’ don’t sound anything alike, and the idea that Kara actually has something inside her body that the Kryptonian council or whoever put there to keep her from having sex is kind of… horrifying. Alex wouldn’t care if Kara didn’t want to have sex, as long as she wasn’t being all high and mighty at Alex about it, but this means she doesn’t even know, can’t make that decision for herself.

Kara loses the rigid Kryptonian posture a little. She gives Alex a suspicious, uncertain look, as if she’s not quite sure why Alex stopped yelling, and grabs at the hem of her shirt again. “Yes,” she says. “Everyone has one, it’s not just me. It was a standard medical procedure.”

Of course it was. God. “You can’t turn it off?” Alex asks. “You don’t have any control over it? What if it breaks?” She’s seized with sudden worry. Her parents hid Kara’s ship somewhere, but other than that, there’s no Kryptonian technology on earth. If Kara has a medical implant—there could be more than one medical implant too, Alex doesn’t know—what happens if something goes wrong?

“I can turn it off,” Kara says. “It’s a safety feature. They wouldn’t leave something inside us and not give doctors a way to disable it.“

Alex breathes out. Good, okay. That’s one less thing to worry about. No need to spend the evening freaking out about how fast she could learn an emergency medical procedure from an advanced dead civilization when she would much rather be annoyed at Kara for interrupting her (admittedly mediocre) first partnered sexual experience.

And then she looks up and Kara is standing right in front of her, wearing only her bright red bra. Alex stumbles back immediately, looking away and squeezing her eyes shut tight. “Kara please put your shirt back on!” Kara has _breasts_ now, and even if she is wearing a bra, that doesn’t mean that isn’t a nudity taboo. Kara should definitely know that by now. Alex runs their conversation back in her mind, trying to think of anything that might have indicated that this would be okay and coming up blank. They were talking about sex. Why would Kara be taking off her shirt?

“I’m showing you the implant,” Kara huffs. “You have to open your eyes to see it.”

Alex opens her eyes immediately—she definitely wants to see the implant. Kara has pulled her head to one side, angling her neck toward Alex and moving her bra strap out of the way a little. Alex doesn’t know what she’s supposed to be looking for at first but then—there’s a small spot where Kara’s skin is just a few shades lighter than the skin around it, about the size of a penny but perfectly square. She never would have noticed it if Kara hadn’t pointed it out.

“That’s it?” Alex asks. “How do you access the controls? Do you have to like... cut your skin away from it?”

“It’s a biometric scan to switch it on and off,” Kara says. “Primitive tech because it’s meant to be done in an emergency.”

“Oh yeah, a biometric scanner under your skin is primitive tech,” Alex scoffs, because of course it is. If Alex could figure out how to make something as advanced as Kara’s implant scan she’d probably win a prize or get tenure somewhere out of it, but for Kara it’s primitive. Kryptonians.

Kara smiles at her, tentative, and Alex can’t help but smile back. They’ve had conversations like this before. For all the annoyances there are perks to living with someone from an advanced civilization, and most of the time Alex is happy to trade minutiae of how life on Earth works for hearing about Krypton. Kara doesn’t always want to talk about it, but when she does, when Alex isn’t too proud to ask, it sounds amazing. Terraforming, genetic engineering on a scale that sounds like magic, and then the small things that were just part of Kara’s world there. Little brown dragons that would hang upside down from the rafters in public buildings, how Kara used to have an actual robot that would wake her when her mother got home so she could see Alura when she wasn’t busy in court. It’s hard to wrap her mind around, that when Alex was in elementary school learning multiplication tables Kara was... well, sleeping in a pod but when she was the age Alex was then, she was visiting other planets.

And now Alex is witnessing some of their miraculous technology for herself, and of course, it’s basically a fancy chastity belt.

“How does it prevent sexual arousal anyway?” Alex asks, scientific curiosity taking over. Kara frowns.

“I’m not sure,” she says. “No one ever told me.” Kara hesitates, staring off into some middle distance for long enough that Alex is about to ask if she’s okay, because sometimes she _isn’t_ , when she’s thinking about Krypton. And then Kara she seems to shake herself out of it. She presses into the spot where the implant is with her thumb, and then forefinger, and then all the other fingers on her hand. There’s a little beep from _beneath Kara’s skin_ , and then nothing.

“I’m going to find out,” Kara says, jaw set. “I mean, I don’t know if I’ll be able to figure out how it works, but... I’m going to find out what sexual arousal feels like.”

Alex stares. Was that... it? Kara has some sort of chastity device on her shoulder and now it’s just off? Just because she felt like it, because she was curious? There’s no way Alex convinced Kara of her point of view that quickly. But then again, Kara is as much of a fan as Alex is of experimentation. It makes sense that she would want to see for herself.

Kara frowns and looks down at her groin, as if that’s where all the action is going to be happening. “I don’t feel any different,” she says, and Alex snorts.

“Whatever that did it’s probably not going to be instantaneous,” she says. “If it’s controlling your hormone production, the hormones are going to need some time to start producing, if it’s distributing a drug to dampen arousal it might need some time to wear off,” a tiny implant producing drugs that could do this seems less likely, but Alex wouldn’t put anything past the Kryptonians, honestly. “I guess if it’s doing something to the connections in your brain that could be pretty quick though. You could try watching some of Dad’s old porn that Mom hasn’t thrown out yet, see if that does anything.”

Kara’s face wrinkles up in disgust, and Alex manages to keep a straight face for all of a second before they’re both laughing.

They watch movies with sex scenes instead, after Alex has that shower, with Alex’s textbooks half-heartedly lain out beside her on the couch so she can at least tell her mom she was studying when she gets home.

Watching TV sex scenes with Kara for the purpose of seeing if Kara will get aroused by them is kind of embarrassing, but it’s less embarrassing than watching porn would be for sure, and it’s kind of _fascinating_ too, because Alex really wants to figure out what exactly that tiny piece of tech was doing to Kara’s body.

Or it would be fascinating if there was any effect. As it turns out, Kara’s reaction to TV sex is the same as it was before—mostly confusion and some covering her face in secondhand embarrassment. Eventually, after they’ve watched a few scenes and nothing happens, they decide to just finish the last movie instead. Maybe Alex was right and it will take a while, or maybe the implant was just a placebo sort of thing to make high-born Kryptonians think they shouldn’t want to have sex. That wouldn’t surprise Alex either, honestly, though it would be a little disappointing to her scientific curiosity. Even so, at least it would mean Kara feels okay wanting to do those things. Alex’s mind shies away from the thought of Kara and sex, but—Kara has lost so much, Alex wants her to have everything she can, on Earth. Everything she wants.

Kara seems genuinely interested in human sexuality too, though she’s a little shy and hesitant about it, probably remembering those earlier conversations about sex and nudity taboos. Or maybe Kryptonians have their own sexuality taboos, which would make sense for a culture that’s (maybe) managed to repress all sexual urges.

Eventually, Kara apologizes for walking in on her. Alex tells her it’s fine. She’s sorry for yelling.

And it’s not _fine_ , but Kara didn’t know. Kara thought Alex was in danger, and she wanted to help her. Alex is just relieved Kara didn’t actually do anything to reveal herself. After the heat of the moment, embarrassment is something she can deal with, at least. Anything happening to Kara isn’t.

*

“I can’t turn it back on,” Kara says as soon as Alex opens the door to their room two weeks later, and Alex feels like she’s going to collapse with relief because Kara is _there_.

It’s the middle of the morning, because Kara just left campus during first period, and the office called Alex down to help find her. This used to happen a lot when Kara first came to Midvale High, running out of classes because the sensory overload was too much, but she’s never left the school before, and Alex spent over an hour searching high and low through the building before she finally thought to try home.

And Kara is here, and she’s fine, and Alex’s heart is still beating rabbit-quick from a whole morning of panic, but—whatever the reason was that Kara left the school, at least she’s okay. And then Alex realizes Kara is _floating_ , and she feels like she can’t breathe.

“What are you doing?” She asks, rushing past her to close the _open blinds_ on their windows, peering through them to make sure no one is out there, that no one saw. Why didn’t Kara close the blinds before she started floating? Why is Kara floating in the first place? They’ve talked about her using her powers. She’s _not supposed to do it_ ,because it’s not safe, and if anyone sees—Alex can’t protect her. (There’s a deep, irrational part of Alex’s brain too, that she can’t seem to make realize that correlation doesn’t equal causation, that can’t help but equate the night she and Kara got in trouble for flying with her dad’s new job, and then... everything else. That if she had been doing a better job looking out for Kara like she was supposed to, maybe her dad would have been safer too.) “Did anyone see you? Please tell me you’ve been staying away from the windows.”

“No, no one saw me,” Kara says, and Alex finally realizes that Kara’s voice is high-pitched and panicked, that her eyes are wide, that she’s scratching at her arms. Something is wrong.

“I can’t turn it back on,” Kara says, and when the words actually penetrate, a sick feeling blooms in the pit of Alex’s stomach. The implant. She has to be talking about the implant. And if Kara’s this distressed about not being able to turn it back on, something must have finally happened, and it must be _bad_.

“I could hold them in at first when they started coming out, but I can’t anymore, and I don’t know what to do. I couldn’t stay in school, I’m sorry,” Kara says, words bleeding into each other.

“It’s fine,” Alex says, putting both hands up, stepping closer to Kara, trying to exude a calm she definitely doesn’t feel. “Coming home was good then. What can’t you hold in, Kara? Is it a... sexual urge?” That was what the implant was supposed to do, right? Alex has been uncomfortably turned on a couple of times before—when she was kissing Jason, when she woke up from some half-remembered dream once—and it never felt like... how Kara looks. But this is a completely new feeling to Kara, if the implant really was stopping sexual arousal. Maybe that’s what’s scary. Scary or not though, Kara needs to control her powers.

And then Kara _changes_.

Her skin seems to ripple, shift, and there’s blue light coming out of her hands, up her arms, all the way to her face, eyes and hair dark with everything else glowing around them. A shimmering, pulsing glow—it looks like some sort of bioluminescence. Kara is blurring too, somehow, the image of her moving in all different directions at once. She’s harder to look at, like she’s not in this reality anymore.

Alex stares, heart hammering. What the _fuck_. Her parents studied Kryptonians, or studied Clark at least, and she’s looked through their notes, and they don’t mention anything like this. This isn’t a thing that just _happens_. And when Alex looks closer she can see it’s... cilia. Thousands, millions of tiny tendrils all over Kara’s _skin_ , shifting and swaying like she’s underwater. All of them moving together to create the strange, etherial effect.

“It’s because of the implant,” Kara says, miserable, and that she still sounds the same is a jarring contrast to the vision of her.

Alex’s first, wild thought is that it must be a mistranslation, or Kara hearing someone wrong on Krypton. The implant must have been to prevent a… sea cucumber response, not a sexual response. But Alex’s parents’ data didn’t include anything about Kryptonian sexuality other than that reproduction was done through their Codex and that Clark was the first natural birth in however long. This might actually be a Kryptonian sexual response. Kara might be the first Kryptonian to experience it in... however long it’s been since they managed to turn it off.

“Look,” Kara says. The cilia pull back from her fingertips and her shoulder—she must be able to control them at least somewhat still—and Kara prods at the implant with each finger, like she did before.

There’s nothing. No beep, no extra special glowing, nothing.

“It _hurts_ ,” Kara says, floating higher, shoulders hunching, and Alex is still reeling but she steps forward automatically, arms out, because Kara is _upset_ , and Alex always feels terrible when Kara is upset. When Kara is upset she wants hugs.

Alex doesn’t even stop to think about how this might be a bad idea, that it might be dangerous to touch Kara like this, until Kara has already stepped into her arms. Kara presses her face into Alex’s neck, and Alex can _feel them_. Hundreds of soft, velvety tendrils moving against her neck at once. It’s a tingling, almost ticklish feeling, like nothing Alex has ever felt before, and her brain struggles through how to even categorize the situation before settling on: weird, but nice. It’s a good thing they’re not stinging, or poisonous to her in some way, because she definitely would have found out too late.

“This feels good,” Kara says after a moment, surprised, and she rubs her face further into Alex’s neck, which feels _definitely nice_ , and her neck being caressed is really not what she needs in the middle of comforting Kara. But Kara is relaxing a little in her arms, starting to lose the tension in her shoulders, and it’s fine, Alex can control her own sexual arousal thank you very much. She’s been controlling it since... well, since she started thinking about sex. Kara not understanding Earth nudity taboos yet _did not help_.

She holds on until Kara, who has in the past asked Alex very specific questions about how long hugging is socially acceptable in different situations, (Kryptonians had a very different and strict public/private divide for things like showing affection and she didn’t want to shame her new alien family) lets go. And when they pull away from each other, the cilia on Kara’s face are glowing a little less, are a little stiller, are fading back into Kara’s skin. They come back a moment later with a pulse of light that makes Kara wince, but—

“Kara,” Alex says. “I think where your—where they were touching me, it got better for a minute. Maybe they need to be touched.”

Kara holds out her arm, hesitant look on her face, and yes, this is something Alex can help test.

She takes hold of Kara’s arm. The cilia there are just as soft and tingly as the ones on her face were, dry and cool to the touch. Alex rubs up and down Kara’s forearm, watching her face for signs of how she’s feeling, if this is a good thing to be doing or not. So far, it looks good. Kara is still visibly in distress but her shoulders are a little looser, face is a little less creased beneath the pulsing blue light. Alex is still trying to figure out how a tiny square on Kara’s shoulder could have been preventing all of this. Were they always under Kara’s skin, just waiting to come out? Did the implant turning off release some sort of hormone causing them to grow? Kara looked normal earlier, but if they grew, does that mean it’ll always hurt for her to keep them withdrawn, or are they out now because it’s some sort of build up of... arousal? Alex‘s hands still.

“When you said it felt good, did you mean like sex good?”

“No,” Kara says, brow furrowed. “I mean, I don’t think so? They’re really sensitive. Like when I got here but worse. Clothes hurt, touching almost anything hurts, but holding them under my skin felt like... this awful pressure building up. This is better, it’s just all...” she’s shaking a little, and Alex’s heart aches. “Everything hurts. Except skin, so far. This is nice.”

“Do you think it... is a sexual response? I mean, do you think there’s a chance the implant could have been doing something else?” Alex asks, hesitant, as she starts rubbing Kara’s arm with her hands again, watches Kara relax. She’s glad she can do something to help, at least. If this is a sexual response, rubbing Kara’s arm doesn’t feel sexual to Alex at least, and if it is to Kara... Alex can just not think about it. When Kara first got here, when she was bombarded by scents and smells and being able to see through people’s clothes and skin, Alex was still annoyed and bitter about Kara barging into her life. She would ignore her when she got overwhelmed, or avoid her because it was awkward, and embarrassing, and Alex feels _awful_ thinking about it now. Kara still gets on her nerves, but she’s Alex’s _family_ , and it’s Alex’s job to protect her. Watching Kara hurting now feels like something sharp and aching in Alex’s chest.

Kara winces a little, looks down at her crotch, like on the day she turned the implant off. “I think that’s the sexual response,” she says.

Alex looks. Kara’s wearing pajama pants, she must have changed when she came home because the jeans she wore to school were irritating her skin too much. All of her clothes are rustling on her a little, with the cilia moving underneath, but there’s something else moving in the juncture between her thighs. Definitely bigger than the cilia, definitely _moving_ , not just like a dick getting hard, and—

Alex drags her eyes away. Kara is having a sexual response. She should not be staring, no matter how curious she is about what that looks like for Kryptonians. This isn’t just something she can research and be apart from, this is Kara being turned on. And if touching the cilia is enough to make them start to go away, or at least hurt less, then if there’s something in Kara’s pants, maybe that needs to be stroked too. 

“I think you need to masturbate,” she tells Kara, trying desperately to pretend this is a casual, normal thing to be telling her, that she doesn’t want to know what that looks like. (Alien sexuality is a line of research Alex has never even considered before, but she’s definitely considering it now.) “I mean if touching the cilia helps, then probably touching, um. If this is all part of a sexual response, maybe that’s what stops it. Did Kryptonians masturbate if they didn’t experience sexual arousal?”

Kara’s face has gone purple with the force of what must be her blushing under the blue, and Alex is glad she isn’t the only one embarrassed by this conversation. “I can figure it out,” she says, starting to float a little again. “I’ve been on Earth for long enough.”

Right, of course. Alex feels like an idiot. “Okay, yeah,” she says, and then realizing she’s still touching Kara’s arm, pulls back, wraps her arms around herself instead. Alex needs to be not in this room anymore. “I’ll give you some privacy.”

*

Downstairs, Alex turns on the TV for noise, but she doesn’t hear any of it.

Kara is upstairs, in pain, touching her alien parts, and that thought makes it hard to concentrate on anything else. Two weeks ago, Alex wouldn’t have been so horrified by a Kryptonian chastity device if she’d known what it was there to prevent. And Alex is trying to take her mind off it, trying to give Kara privacy, but all she can think about is how useless she feels, not being able to do anything to help. And worse, what if it doesn’t work? When Kara pressed her face into Alex’s neck, when Alex touched her arm, she definitely felt better, and the cilia definitely started to fade, but that doesn’t actually mean that touching them a lot will make them go away. What if they have to go to Eliza and tell her about what happened, that Kara wanted to experience sexuality and Alex didn’t stop her from turning this implant off, because Alex’s mom would definitely blame her. What if Kara is going to be blue and glowing forever? She wouldn’t be able to go back to school, she wouldn’t be able to go _anywhere_... Alex wouldn’t be able to protect her.

On the television, two people are kissing, and Alex turns it off, puts her head in her hands, twisting feeling in her stomach. And then she hears it—sound floating down from upstairs. Kara is crying.

*

Upstairs, Kara is lying back on her bed, hovering just above it. She’s naked, and the cilia are _everywhere_ —down the column of her neck, gathering around her breasts, her feet, her thighs. She has whatever organ was moving there earlier clasped in one hand while she runs the other roughly up her arm, trying to smooth the cilia back like Alex did earlier. They’re still glowing, as bright as they were before.

She’s shaking with sobs, awkwardly contorted to muffle them in the crook of one of the arms she’s using to stroke herself.

Alex feels like the floor has opened up beneath her. Whatever Kara has been doing, it doesn’t look like it’s been working, and she’s hurting—really hurting. It doesn’t make any sense, it was working before when Alex touched her, but maybe that’s because the cilia are different than Kara’s... whatever else it is she’s touching.

“Kara,” she says, keeps her voice soft because when Kara’s overwhelmed sometimes even normal speaking volume is too much for her. “Are you okay?”

At her voice Kara flinches. The glow flickers brighter and she floats upright, curling around herself, using both hands to cover whatever it is between her legs. Not like a penis, Alex saw it _move_ , but she didn’t get a good enough look to have any other guesses. It doesn’t matter anyway.

“Alex,” Kara’s voice is hoarse, and Alex thinks her eyes might be red but the light everywhere else makes it hard to tell, makes them look deep and fathomless. “What are you doing here?” She doesn’t sound mad, just curious, which is great because Kara is naked, and Alex told her she wouldn’t come up, but she’s here anyway. Kara looks too miserable to be angry.

“I came to see if you needed help,” Alex says, feeling awkward as soon as the words are out of her mouth, but it’s the truth. There has to be something Alex can do, because she can’t stand just listening to Kara in pain. “Can I get you some soft blankets, or run you a bath or something? You sounded like you were having, um, trouble, and...” she twists her hands uselessly in the air.

“Blankets all hurt,” Kara manages. “I don’t think a bath will...” Alex watches Kara struggle for words to turn down the bath too, and then realizes—there is something she can do, and she knows it works.

“Do you want a massage?” Alex asks. “I know it helped earlier when I touched your arm, so if you lie on your stomach I can... massage, see if it helps? And then I can go downstairs again so you can finish?” If Kara lies on her front, at least Alex won’t be face to face with the more embarrassing nudity. Part of Alex thinks she should just go downstairs now. Kara was _masturbating_ , Kara is still holding onto her junk, though that’s probably mostly to shield it from view—but the thought of Kara blue forever is still at the front of her mind. Whatever she can do to help, she needs to do it.

Kara stares at her for another moment and then her shoulders sag. She rolls herself over in the air and lowers herself to the bed, winces when she makes contact. Her regular duvet is the softest one Eliza can find—Alex can’t imagine how sensitive the cilia must be for that to hurt.

“Please,” Kara says, voice muffled in the blankets, and Alex feels a rush of relief, hurries over to the bed. It’s awkward, arranging herself kneeling beside Kara but not touching her with her too-scratchy jeans, but eventually she figures out she’ll be able to balance herself on Kara, and she falls forward a little, presses into Kara’s shoulders with both hands.

The cilia are velvety and cool to the touch here too, a strange contrast to how Kara always feels warm when she snuggles up to Alex on the couch. Pushing on them deliberately feels different than just stroking them did earlier—they resist under the pressure of her hands. She’s careful at first, mindful of Kara’s wriggling and doing her best not to look further down than the small of Kara’s back, because even though she’s fascinated by the cilia, Kara is naked and clearly in distress and Alex doesn’t want to be creepy.

And then Kara says, “harder, please.” Alex digs the heel of her hand into Kara’s lower back, and the cilia’s resistance gives under the pressure—she can almost feel them grabbing at her palms as she digs in. Kara _melts_ , tension draining out of her, and Alex sags forward too, losing some of the tightness in her shoulders she didn’t realize she was carrying. It’s working. Alex wasn’t really sure what she was offering when she told Kara she could give her a massage—mostly a less weird way to say _I can touch your back if you want_ , but applying firmer pressure makes it feel more like a normal massage, and Alex at least sort of knows how to give one of those.

It keeps working too. Kara makes less distressed noises, more little murmurs of pleasure, and Alex hesitates for a moment over her butt before just... keeping going. It’s a massage. It’s fine. She’s not touching Kara’s butt, she’s massaging the cilia that happen to be on her butt, because the cilia are everywhere. They’re still out, but where Alex has touched them they look less agitated, are glowing less.

Alex moves down Kara’s thighs too, trying to ignore her racing heartbeat, and when she finishes with Kara’s ankles and feet she pulls back. Massage accomplished. Only Kara starts to turn over, and... right. She’s only massaged half of the cilia. She hadn’t thought about touching Kara’s front too, but as Kara moves she can see the difference between the cilia that have been massaged and those that haven’t, how the ones she’s touched are dimmer, stiller. It would definitely help, to keep going. Kara tenses when she catches sight of Alex’s face, and Alex does her best to rearrange her features so they look like she’s fine, because she is.

“Do you want me to do your front?” She asks.

“Yes,” Kara says after a moment’s hesitation. “If that’s okay.”

“Yeah,” Alex says, tongue thick in her mouth, and Kara finishes turning, carefully covering her crotch area with one hand still, settles onto her back with much less wincing than when she first lay down on the bed. Her (glowing, blue) boobs are _right there_ , and Alex takes a deep breath, does her best not to stare. It’s a massage. She’s helping.

Trying to figure out where to start is overwhelming though, because nowhere on her front seems like a neutral place to touch Kara until she realizes—they’re on her face too. That seems safe.

Alex leans in, strokes Kara’s forehead with firm fingertips, watches the cilia start to calm under her touch. She rubs across her cheeks, down the bridge of Kara’s nose, and then across her chin, and Kara stares up at her, gaze glassy. It feels intimate in a way Alex wasn’t expecting. It’s the closest she has ever been to Kara, Kara who’s completely relaxed underneath her. Despite the circumstances, having Kara trust her to do this warms something inside her, makes the still nervous part of her swell with affection. Kara smiles at her a little when Alex is touching her lips, shaky but warm, and Alex smiles back. It’s the two of them, in this together. It makes it a little easier to keep going.

And it’s fine, moving down Kara’s neck, across her shoulders, her collarbone, and then Alex is at her chest, and it doesn’t feel as fine anymore. Her heart pounds, and she hopes Kara isn’t paying attention to that right now. It’s fine to massage her foster sister’s breast if she avoids the nipple, right? If she’s hurt and happens to be an alien especially? Kara gasps, arches a little when Alex goes too far down her chest, too close, but she doesn’t say to stop, doesn’t say anything, and—fuck, is Kara having a sexual response from this? Alex’s heart races and her hands shake a little, and she stares at Kara’s breasts, because if she looks away she might touch nipple by accident and that would be _worse_. Is that an erogenous zone for Kryptonians too? If Kara had a reaction to Alex touching her breasts then probably. Kara has nice breasts, even pulsing with billowing cilia. 

It’s a relief to be able to move further down her body. Touching Kara’s belly feels like a lot too, but it’s definitely easier.

Then she’s past that and she hesitates at where Kara’s hand is blocking the juncture between her legs. Alex starts at the ankle instead, moving up. She needs time to stop freaking out. This isn’t a sex thing. It’s just... a naked massage to try to calm Kara’s alien sexual response. The cilia tense and squirm and then relax under Alex’s fingers, a little like working out muscle knots.

And then by the time Alex gets back to upper thigh again, Kara’s grip on her whatever-it-is has loosened enough that it wriggles out of her grasp, brushes against Alex’s hand.

Alex jerks back and stares. It’s thin and eel-like, blue all over, and—Kara, flushed, grabs it with her hand to hide it from Alex’s gaze, pins it to her stomach.

“Sorry,” Kara gasps. “I’m so sorry.”

“What is it?” Alex asks. She feels strange, hazy, like giving the massage has been meditative for her too. It’s clearly Kara’s genitalia that she’s covering, obvious if not by the location (alien genitalia could technically be anywhere) then because it was the thing she was touching when she was trying to come. Kara is naked, and her junk touched Alex, and all of this makes it feel like this is a question she can ask, even though it probably shouldn’t be.

“It’s, um... it’s called an arral,” Kara says, voice dipping into the accent she had when she first came to stay with them, rolling the ‘r’ a little. “It’s what we used for reproduction before the Codex. I think I need to make it, um, ejaculate.”

Right. Kara was up here trying to masturbate before Alex came up before she heard her crying. This is absolutely a sex thing. Kara actually needs to make herself come to get the cilia to go away, if they’re right about what will do it. So Alex needs to leave. She shouldn’t be here in this room with Kara lying naked on the bed. She shifts to get up, and her heart drops into her stomach. She shouldn’t be slick between her thighs from this.

“It wasn’t working,” Kara says, staring up at the ceiling. “I was touching it, and it felt good, but it wasn’t enough. There was pressure, but I couldn’t make it... release.”

She couldn’t make herself come. That’s what needs to happen, it must be, for Kara to be able to pull the cilia back in, to look human again. Alex watches Kara sit up on the bed and curl around herself, pulling her knees up to hide both her breasts and her arral. With the cilia calmer than they were earlier, she can see tear tracks on Kara’s face. If Kara doesn’t get the cilia to go away, she’s going to keep hurting.

Part of Alex knows she should go back downstairs, should go back to her parents’ research on Kryptonians, should call her mom, even, or Clark, if Kara still isn’t able to come, to see if they have other ideas. They’ve done all they can.

But they haven’t really.

Slowly, heart racing, mouth suddenly dry, Alex steps off the bed and sinks to her knees in front of it.

Kara shifts forward, looks at Alex in confusion, and Alex feels like she’s going to pass out. Like she should run. This is an awful idea. She shouldn’t be doing this. But she _has to fix this_.

“Let me help?” She asks Kara.

Watching the moment Kara realizes what she’s offering is like watching a car crash in slow motion, and Alex can’t look away. She just offered to blow her foster sister, and even if Kara is an alien, even if Alex is only offering because Kara is _blue_ right now, because Alex wants to protect her, she still thinks Kara might be disgusted with her for this.

Kara looks—shocked, horrified, and something else too. It’s harder to read her expressions beneath the swaying cilia, the flickering blue light, and maybe those reactions are saying something too, but if they are, Alex has no idea what.

“Alex, you don’t have to,” Kara says.

Alex stays where she is, looking up at Kara, her sweating palms on her thighs. It isn’t a no.

“It’s okay if you don’t want me to,” Alex says. “But if your hand wasn’t working, then. I mean. We have no idea what might work, especially since people on Krypton didn’t have arrals anymore, but—“ Alex feels like her face is going to catch flame. Kara is still _staring_ at her, and Alex is making an argument for why she should put her mouth on her junk. “On Earth, humans like someone else’s mouth on their genitalia.”

At least Jason had—which is maybe a terrible comparison because what Kara has isn’t human at all, but it’s the only one Alex has. Alex feels like she’s going to _die_. Kara’s face is still other than the flickering cilia.

“I want to help,” Alex says, because she _does_ , she wants Kara not to hurt anymore, she wants Kara to be able to look human again, to pass, be safe. She carefully tries to think just about the act itself, not everything else attached to it. It doesn’t have to mean she’s attracted to Kara.

And it won’t be that different, right? She didn’t really like giving Jason the blowjob, but it was fine. Other than Kara walking in, and... all the rest of it. It wasn’t that hard, at least, even though she hadn’t had a chance to do research beforehand because it had just come up. She grabbed onto his penis with one hand, and put it in her mouth, and sucked on it for a while. He seemed to like it. If Kara’s hand wasn’t stimulating enough on her arral, it makes sense that maybe a mouth would be better. Able to cover more surface area at once, and do suction, and... resemble a warm, wet place a Kryptonian might stick it to reproduce with another Kryptonian, however that works. It’s not like Kara can suck herself off, unless there’s something about Kryptonian flexibility that Alex hasn’t heard about either.

Alex blew Jason Kelly because she was curious. She can blow Kara because she loves her. And Kara’s here, so she can’t walk in. (Eliza getting off work early and walking in is too horrifying to think about.) It makes sense. Alex’s discomfort doesn’t make sense, the heavy feeling between her legs doesn’t make sense either—this wouldn’t be doing anything for her—so she can just ignore those things. It’s fine.

“Okay,” Kara says, voice small. “Please.” She shuffles forward so her ass is at the edge of the bed and uncurls slowly. Drops her knees and dangles her feet off the edge of the bed. Her shoulders are still a little hunched but she takes her hand away from where it’s holding her arral, slow and cautious, and Alex gets her first good look at it.

Kara’s arral is glowing too, like the cilia, bioluminescent light flickering down its length. It’s blue all over, not just overlaid with it from the cilia—it’s not covered in any. Now that Alex can really see it moving it looks prehensile too. About the same thickness as Jason’s dick, maybe a little thicker (and Alex hates that this is her only point of comparison), but it’s longer, coming out of Kara’s—whatever the Kryptonian equivalent of a vagina is. There’s a dark blue stripe going up the bottom of it, and for a moment Alex thinks she sees it open. Are there cilia _inside_ of it?

“You don’t have to,” Kara says, shifting back, lifting one foot off the ground like she’s going to curl in on herself again, and shit, Alex was staring too long. “I know it’s—“

“It’s beautiful,” Alex says, and then flushes again, because _fuck_ , that was a stupid thing to say. It _is_ beautiful, especially compared to weird wrinkly human penises, but that doesn’t mean she should be telling her foster sister her junk is beautiful. She should stop talking.

She reaches out and wraps her hand around the base of it instead. Kara gasps, rocks forward. The arral is hot and slick in Alex’s hand—it must be self-lubricating, and… Alex doesn’t have time to think about xenobiology right now. She takes a deep breath, leans in. She doesn’t look at Kara’s face. She’s afraid if she catches her eye, sees Kara looking back at her, she’ll chicken out, or Kara will see something in Alex that will make her not want to do this after all. Alex wants to do this.

She bobs her head down, tries to get her mouth over the top of it, closes her eyes at the last second, one last moment of, is she really going to do this? She misses, gets a mouthful of the side of it and her own hand instead. The arral is swaying off to the side—it’s definitely prehensile, it must have moved out of the way. The cilia on Kara’s inner thigh, on the swell of her mound are glowing brightly, places Alex didn’t touch earlier. She touches Kara there now with her other hand, kneads with careful fingers as she draws back to try a second time to take the arral in her mouth.

Kara whimpers in the back of her throat at the touch, and the tip of the arral moves to Alex instead. It runs across her lips, pushing a little at the seam, and Alex is wet, wet, not thinking about it. She opens for it, lets it squirm into her mouth and then draws her lips tight and sucks.

“Ah!” Kara cries out, hips jerking, and Alex looks up, for a moment terrified she’s done something wrong. Kara is leaning back on her palms on the bed, head tipped back, cilia rippling along her arched throat, her mouth hanging open. The lights flicker faster along her face, but they’re no brighter than they were before. She looks beautiful.

Her arral is hot in Alex’s mouth, like a brand. It tastes salty, briny almost, but meaty too, slippery and _alive_ —it’s still moving even though Alex has stilled, lashing along her cheeks, her gums. _She has Kara in her mouth_.

“I’m okay,” Kara says, voice strangled, knowing the question before Alex can pull back to ask it. “It feels good. You can keep going.”

That’s good. Maybe this will work then. Jason’s dick had been musty, a little smelly, and overall, like sucking on someone else’s skin. This is much more pleasant, and _interesting_ too. The thought that feeling good is something Alex can give Kara is a warm rush spreading through her.

Alex sucks, hollows out her cheeks to draw the tip of the arral into the middle of her mouth and massages the bottom of it with her tongue, trapping it against the roof of her mouth. She rubs at the juncture of Kara’s thigh, works her fingers toward the base of her arral, and Kara gasps, squirms above her. Kara is enjoying this, enjoying Alex’s mouth on her.

Alex presses her thighs together, trying to ignore the way her pulse pounds low in her belly and between her legs, hoping Kara doesn’t notice. She gets to work.

Time starts to slip. The floor in their room is hard under Alex’s knees, but Kara’s arral is warm in her mouth, and Kara’s thighs tremble under her hands. Alex tries different things—bobbing her head (like she tried with Jason, his hand in her hair), drawing off and licking up the length of it, holding it still with her hands as it thrashes, sucking in as much of it as she can even though the full length is too much to fit in her mouth. She strokes, kneads at the cilia along Kara’s inner thighs, her vulva, her lower belly, tugs at her nipples when Kara leans forward enough (Kara shudders forward, chokes out a sob)—all of the places that had been too _much_ to touch, earlier.

It’s quiet in the room, other than Kara’s little cries, the quickening rain on their windows, the wet sucking sounds of Alex’s mouth. Alex’s jaw aches from holding it open, but the lubrication from Kara’s arral keeps her mouth from getting dry, and Alex licks, and sucks, and swallows, and loses herself.

At some point when she pulls off, the seam of Kara’s arral opens, and closes around her tongue, massaging it with its inner cilia. There’s suction too, and it feels _good_ —Alex leans into the sensation, lets the cilia in Kara’s arral pull at her tongue as the cilia on Kara’s thigh are pulling at her fingers. When she eventually pulls back, Kara’s arral is still fluttering open and Alex can lick, run her thumbs along the tingling cilia inside of it.

There’s something that feels right about this, being on her knees in front of Kara, making her whimper, thrash a little, and when Kara strokes Alex’s hair with one shaky hand, Alex feels the throbbing in her own core intensify, the ocean inside of her swell. This is what she wants to be doing. Bowed in supplication, diligent to her task. Even though her knees and jaw ache, part of her thinks she could stay here forever, as long as she could be making Kara happy.

With Jason, she felt so far away from him, on her knees with his dick in her mouth, like they had disengaged from where they were, kissing, when he pulled his pants down, when she stepped away. Doing this for Kara, though, she feels _close_ to her—she can feel the minute movements of her muscles as she shifts, taste her, smell her, be surrounded by her.

And then Kara cries out, louder than before, and her hips jerk. A rush of fluid spurts out into Alex’s mouth, salt water on her tongue, and Alex coughs, swallows automatically. She keeps swallowing, slurping up all of it she can, even as Kara is stammering an apology. Alex doesn’t want any to get on the floor, on the bed, doesn’t know if it would stain. Some of it escapes her mouth anyway, leaking down the sides of Kara’s arral to the cilia on her groin, to the bed, and Alex does her best to catch it with her hands, stop the mess. She wants it all.

She told Jason not to come in her mouth, but for Kara she swallows, _wants_ to swallow. With Kara, disgust doesn’t roil in her stomach and tighten her throat. It feels a little like penance, a little like devotion.

Eventually, when Alex has licked up all of the blue-tinged fluid she can, off her hands, off Kara’s arral, around the base of it, lapping all the way down to where it comes out of her, she pulls back, reluctant, wipes her mouth with the back of her hand. Looks up.

Kara has fallen back on her elbows against the bed, hair mussed, cilia smaller, only flickering with the barest hints of light. Her eyes are bright with wonder, and she grins at Alex, and Alex can’t help but grin back, the worry in the back of her mind starting to calm. She made Kara come. The cilia are pulling back, slowly, and Kara looks _happy_ , and Alex _did that_.

“It worked!” Kara says. “I mean, I’ve never had that happen before, but, that was an orgasm, right? The definitions I’ve seen for the human orgasm include that it’s the peak of sexual excitement, with vaginal contractions or ejaculation. That was ejaculation, and I definitely felt a release of tension, and I’m so sorry, I didn’t mean to make you swallow it, but... thank you,” she’s looking at Alex like Alex has done something amazing, and Alex’s chest hurts with it.

“That was an orgasm,” Alex says, and can’t help throw in a “nerd,” even if it’s said with fondness, because she knew Kara was researching human sexuality but she wasn’t expecting definitions out of a textbook. What just happened fits the definition for humans. There was definitely ejaculation, and Kara’s arral is half-retracted now, undulating gently against her thigh, not all the way out and thrashing like it was earlier.

“Takes one to know one,” Kara says, but she’s smiling too. Alex wants to reach out and run her hands along the cilia again, feel Kara relax under her touch. It feels like some wondrous new power, being able to do that for Kara, and Alex feels like she’s floating, like she’s drunk on it.

“Do you feel better now?” Alex asks. “Can you pull them back in?” The cilia have definitely retracted, but they’re not gone yet. Alex wonders if they will go away completely, or if they’ll just be another sort of power Kara has control over. Sea cucumber mode, with bonus external genitalia.

“I feel a lot better,” Kara says. “I think I can pull them in now.” She looks down at Alex with a sad sort of smile that feels... not quite right, though Alex can’t put her finger on why. “Thank you for doing that, Alex.” The not-quite-right feeling is something about the way Kara has thanked her, too. It doesn’t matter.

Kara closes her eyes, crinkle furrowing between her brows, and the cilia start to sway and glow a little again.

Alex watches, and waits, and her knees start to hurt again, because she hasn’t moved, she’s still kneeling in front of Kara. And the blowjob worked, Kara came in her mouth and she swallowed it, but... the cilia still aren’t gone. Dread opens up in the pit of her stomach. She knows before Kara opens her eyes, looks across at her, stricken.

“I can’t pull them in,” Kara says. “It still hurts to try. I don’t understand.”

Alex thinks she might. Her parents are (were) scientists, she’s going to be a scientist one day too. She knows about experimentation, the scientific method. The massage made the cilia start to retract, the blowjob almost got rid of them completely. It’s just… not enough yet.

“I think we have to do it again,” Alex says, staring up at Kara. “If it’s a release, of tension, of… something building up in your system we don’t know about, I think there’s more that needs releasing. But my jaw is tired, and my knees—“ are suddenly unbearable to be sitting on. She shifts to her side, falls on her ass and scrambles to her feet, thighs sticking uncomfortable together. She’s dripping wet and swollen just from taking Kara into her mouth, and she hopes Kara doesn’t notice, doesn’t hear it in the way Alex moves. It’s exciting and frightening all at once. This is how Alex thought she would feel about sex, when it happened with Jason, but didn’t, and she’s feeling it now, but it’s with Kara. Kara who’s an alien, Kara who’s her foster sister… Kara who Alex wants to protect, doesn’t want to hurt. “I think we should have penetrative, arral-vaginal sex. I think you should put your arral inside me.”

When she looks back at Kara, Kara looks stricken, and Alex’s heart drops into her stomach. Oh no. Kara seemed to enjoy the blowjob but that doesn’t have to mean she’d want to do anything else. But Alex doesn’t know what else they can try. If Kara doesn’t want to do this, she can lie on the bed, maybe, get Kara to position herself beside her, suck for as long as her jaw can take, but she’s not sure how long that would be.

“Do you want to do it?” Kara asks, hesitant. “I don’t want to make you…”

Make you. There’s that phrase again. Alex realizes with a sick feeling—Kara doesn’t think she wanted to do this in the first place. Why should she have wanted to? Kara is her foster sister, and Alex took her in her mouth, and swallowed. What does it say about Alex, that this is her second blowjob in two weeks, and more than that, that she’s soaking wet from blowing Kara while making out with Jason, having him actually touch her, only made her a little damp and uncomfortable?

But none of that matters right now. Alex can shove it down, doesn’t have to think about it. What matters is protecting Kara, and protecting Kara means having sex with her again, if Kara wants that. If Kara doesn’t want it because she thinks Alex didn’t, then Alex is going to have to tell her differently.

“I do,” Alex says. It’s harder, feels more awkward to say out loud than it was to do it. She has to force the rest of the words out: “Blowing you made me sexually aroused.” Oh god. Alex squeezes her eyes shut tight for a minute, mortified. She could not be more uncool if she tried. She should have just said blowing Kara made her horny, like a normal person. Can Kara smell her, too? It’s something Alex has never considered before, and the thought of it is more embarrassing than it should be, with Kara’s cum heavy in her belly.

“Really?” Kara asks, and she’s flushed too, more red, less purple than before with the cilia faded. “Even though there wasn’t any stimulation for you?”

“I liked putting my mouth on you,” Alex says, turns away because she can’t do it, she can’t look at Kara while she’s saying these things. She watches the rain through the cracks in the blinds instead, thinks about that time Kara took her flying, how her heart was beating as fast then as it is now. “I liked being on my knees for you. They hurt now, but it was...” it was _good_. It felt right. Alex can’t keep thinking about it now, feels small under Kara’s regard, even if it’s just her curiosity, not... disgust, disdain, any of the things Kara’s people, who gave her the implant in the first place, might have thought about what they just did together. Maybe that’s the problem.

“Do you want to do this?” Alex asks. “I know you turned off your implant because you were curious, but we didn’t talk about... you didn’t say you actually wanted to have sex.” And they’ve already had sex. But it’s better to have this conversation late than not at all.

“I wanted to have sex,” Kara says. “I mean, I might not have been thinking about doing it this soon after turning the implant off, but I... yes. I wanted to.” Alex is relieved that it’s something Kara wanted even before turning the implant off, before experiencing sexual arousal, even if she’s not sure why Kara would want that. Sex with Kara just now was... wonderful, but without feeling the arousal in the moment, just looking at it on paper, Alex isn’t sure what there is to desire about it. Two sweaty bodies moving together, getting bodily fluids on each other. Alex does experience arousal though, so the thought of doing that with Kara—in a different configuration this time—is as exciting as it is terrifying.

“Do you want to have sex with me?” Kara asks, and Alex turns to face her. Kara is sitting with her knees pulled up again, hair curtaining her face, and she looks so young and vulnerable like this.

“Yes,” Alex tells her. She’s not sure why Kara’s asking again, but she does, and if she needs reassurance, Alex will give it to her. “I wanted to have sex too, and it‘s felt good so far, and—I want you to be able to leave the house and be safe.” Her heart hurts, looking at Kara like this. It’s weird, and kind of unfair, that she looks just as beautiful with the cilia as without them, just in a different way—alien beauty, a strange goddess. But like this, Kara is trapped here. “I want you to stop hurting.”

Alex always wants to protect Kara. If Kara were a vampire, and needed to suck her blood to be okay, she would let her do that too. It’s kind of a bonus that this is something that’s felt good for Alex too, that probably will feel good for Alex—she’s nervous and excited and really curious, from a scientific standpoint, what it will feel like, having Kara’s arral inside of her. But even if it she didn’t think it would feel good, she’d still do it. She wants to give Kara her body. She wants to give Kara everything. It scares her, sometimes, but—this is a good thing. It has to be.

It feels like something they should talk about more, what it means that they’re doing this, that they like it—what it will mean, after, but for the moment, Kara is still blue, and the only thing Alex can think about is helping.

Kara is still looking at her, searching. Alex doesn’t know what she’s looking for, what she sees on Alex’s face. Flushed cheeks, bruised mouth, mussed hair. But Kara smiles a little—Alex can’t tell if it’s a happy smile or a sad one, through the slowly flickering tendrils across her face—and says, “okay.”

*

Penetrative sex means logistics. Kara asks, flushed purple again, if Alex wouldn’t mind taking her clothes off, because anything other than skin on skin contact seems to irritate the cilia, which is why Kara has been floating so much. “They’re called udhivi,” she tells Alex. “That was the name for them when my ancestors had them. I think, anyway. I remember reading about something like this in an old text my mother brought home once.”

Alex, in the middle of pulling her jeans and underwear down, trying her best not to be self-conscious, stops and stares at Kara. “Wait. Are you saying your mom brought home ancient porn?” It seems like it would be completely at odds with all that Alex has heard about Krypton, and Alura Zor-El in particular, but… maybe on a planet where they stopped themselves from experiencing sexual arousal, porn was just a curiosity?

“No!” Kara yelps, Kryptonian dignity clearly offended. “It was an epic poem. A romance, but there was no sex. I think the udhivi were when he was revealing himself in all his true glory, to be one with his kin and… oh no. Maybe it was porn.”

“Were there any metaphors about reaching the heights of their desire for each other?” Alex asks, grinning. “Their true devotion?” But, devotion feels a little close to home. Even if she was the one to suggest this, it feels overwhelming, just taking her clothes off in front of Kara—like peeling off her skin and revealing her inner self, even though Kara has always seen right through her. Alex is glad of the distraction, hopes maybe it will keep Kara from noticing the tacky sheen of her arousal on her thighs, even though—that’s the point of sex, isn’t it? For both partners to be aroused, to get off with each other?

Kara’s arral is extended all the way again, curling up toward her belly, weeping at the seam a little, and, as Alex finally drops her bra and tosses it in the direction of her bed, she wonders if it’s just something to do with the implant, or if maybe it’s because of _her_.

Even though Kara agreed to do this, said she wanted to have sex, even though Alex told her she wants to too—and does, especially if it means _helping_ Kara, Alex feels like they’re teetering on the edge of a precipice, like even taking Kara’s arral into her mouth was a push, like taking her into her body might make them both fall.

It’s nothing like she pictured her first time being—or any time being, for that matter. When Alex started thinking about sex, it was a mental image of dinner and a movie, a hotel room, a boy who looked a lot like Jason Kelly buying a hotel room, kissing on the bed, and… fade to black. Not a conversation with Kara about where they should lie, how they should arrange themselves—it should be on Kara’s bed, because it’s already sort of wrecked from Kara ripping her sheets earlier when Alex gave her the blowjob, and Kara should lie on top of Alex, because even the soft blankets are scratchy against her skin but Alex’s skin on hers felt good—she blushes a little admitting it.

So Alex lies back on Kara’s bed, naked ass on the rumpled sheets, heart pounding like something’s coming for her, even though it’s just Kara. Alex wanted to have sex, even if she didn’t picture it going like this, and it will be _fine_. She lets her legs fall apart after a moment, fighting the urge to clench them together and hide her slick, weeping flesh from Kara’s gaze, because Kara is going to have to lie between her thighs for this anyway. That’s the plan.

Kara floats over, like she’s swimming through the air, the movements too precise to seem like flight to Alex’s mind. She hovers a foot above Alex, dark blonde hair hanging down to tickle Alex’s face, her eyes searching.

Alex forgets sometimes, not that Kara’s an alien but what it means. Clark, who used to come visit her parents, was an alien, but all that meant was the explanation for his superhero powers. With Kara it means a different language, memories of a different world, and now this. Looking down at Alex with cilia rippling across her furrowed brows and pinched mouth, blue light flickering like the sun reaching Alex underwater, it’s the most alien she’s ever looked. And Alex is nervous, but she’s not afraid of Kara, could never be afraid of Kara.

“You’re sure you want to do this?” Kara whispers, like the moment is fragile, like if she talks too loudly she could shatter it. “Your heartbeat is really fast.”

Alex huffs breathy laughter. Of course now is when Kara would remark on the fact that Alex feels like she’s been courting heart failure since she first stepped back into the room. “I’m nervous, but it’s good nervous,” she tells her. “This is new to me.” And it’s important, too. It has to work. Alex can’t think about the alternative.

“Me too,” Kara says, hint of a smile cracking through the blue mask of worry she’s wearing.

Alex rolls her eyes, impossibly fond. “Nerd,” she says, reaching up to flick Kara’s nose.

Kara smiles briefly again at that, and then she takes a deep breath and sinks slowly down on top of Alex.

Alex gasps when she makes contact. The udhivi are all _moving_ against her skin, and it was one thing feeling it under her hands, but against her belly, her thighs, it feels all consuming. A tingling, sliding feeling that’s just this side of ticklish, feels almost like a caress. And Kara’s breasts are pressed against her breasts, and she’s so _heavy_ , pushing Alex down against the mattress. It’s like nothing she’s ever felt before, and it takes her conscious brain a minute to catch up to what her body clearly has realized immediately—it feels good. She’s warm all over, even against the cool udhivi, and so aroused she aches with it. How is she so turned on just from this?

Kara’s quickening breath is loud in Alex’s ear, but she’s not moving otherwise, just lying there. “Are you okay?” Alex asks, immediately concerned. She wriggles her arms out from under Kara’s and wraps them around Kara’s back in as firm a hug as she can manage, rubs the cilia along her spine. She wonders if Kara is scared too. The thought makes her feel a little better even as she desperately yearns to comfort.

“I’m fine,” Kara says, voice high and tight, pressing her face into Alex’s neck. “It’s... it feels good.” Alex is glad Kara can’t see the blush on her face at her words. Her body is alight, tingling with sensation wherever Kara is touching her, and she’s glad it feels good for Kara too. It’s a good sign.

“You can put it in me,” Alex says, willing her voice to steadiness. “I’m ready.” She has no idea if she’s ready or not. Part of her brain is still running through all of the ways this could be a bad idea, the tests they should have run first—even if swallowing Kara’s ejaculate was fine, will it be fine in her vaginal passage? Will Kara fit? Will it hurt? But the rest of her doesn’t care about any of that, as long as it _works_ , as long as it means Kara’s okay. Alex will do whatever she needs to, whatever Kara will let her.

“Okay,” Kara says, voice breathy. Her arral is slippery again where it’s undulating gently against Alex’s thigh, sliding through Alex’s slick there with its own wetness. Alex spreads her legs a little more, tries to move her pelvis closer to where the tip of it is, even though that’s a moving target.

Kara takes a deep, shuddering breath against Alex’s neck, and then her arral moves, running along the minimal space between their bodies and wriggling between Alex’s labia. Alex turns to bury her head in the sheets, overwhelmed and still a little embarrassed. Kara’s junk is touching her junk. It flutters against her, tip running all over the inside of Alex’s vulva, like it’s mapping it, and she’s dripping, burning for it.

And then it jabs at her and Alex cries out in pain before she can stop herself.

“Sorry!” Kara says, pushing herself up with both arms to look down at their bodies, at Alex, face creased in distress. “Oh no, I’m so sorry, are you okay?”

“I’m fine,” Alex says. The pain is already fading, it was just unexpected, a sharp contrast to how good she was feeling moments before. “There’s a hole, you just missed.”

“Right, okay,” Kara says.

She feels around with the tip, tries and misses again, and it _hurts_. However much sensation Kara has in her arral, it’s clearly not enough. Alex fumbles around to grab Kara’s hand and tugs it down there. She finds the opening herself and then presses one of Kara’s fingers there so she can feel it too. “Here,” she says.

She only realizes how weird _that_ feels when she moves her hand away and Kara is still pressing into her lightly with her pointer finger, looking at Alex like, is this right? And it shouldn’t feel more intimate with Kara’s hand than with her alien sex part, but—Alex has held Kara’s hands. She’s been hugged with them, has put them on her arm to show Kara the appropriate level of pressure to touch someone with, and now they’re in Alex’s vagina.

“Okay,” Kara says, and she’s so close Alex can feel her breath on her face as she speaks. She doesn’t move her hand away until her arral is right there, and then it pushes again, but this time it keeps pushing, and there’s this burning, stretching sensation, and Alex feels heavy, full, and Kara is inside of her.

Kara is _inside of her_.

She can feel every twitch of Kara’s arral, the tension in Kara’s hips pressed against hers, Kara’s udhivi touching her all over, where she’s not pressed to the bed. She’s enveloped, surrounded by Kara, weighted down, tethered by the feeling of her inside, and it’s all so _much_ , Alex feels like her lungs are burning, like she needs to catch her breath from it.

“Are you okay?” Kara asks, wide eyes crinkling with concern, and looking up at her while she’s _inside of Alex_ is even more overwhelming. Sex with Kara. Kara’s alien sex parts are inside her, and Alex feels _good_ , feels like this is exactly where she wants to be—being here with Kara, sharing shaky breaths with her.

“I’m fine,” Alex says, manages a smile, doesn’t have words for the roaring tide inside of her, the way it feels like her whole body is surging with it.

“Okay,” Kara says, smile flashing. “Good. I’m just going to...” And then she leans down again, chest, belly pressed to Alex’s, face buried in Alex’s hair—slowly, like she’s giving Alex the chance to tell her to stop even as she’s trying to get as close as possible. And it’s a _lot_ , this immersion, Alex sinking underneath Kara, like Kara is anchoring her down, but she can’t let Kara stop. Kara needs to do this to feel better.

“I’m good,” Alex says, staring up at the ceiling, the faint light from the closed blinds, rubbing at the udhivi at the back of Kara’s neck. “Just… do whatever you need to do, okay? This is about you getting off.” However good it feels to Alex along the way is incidental.

Kara jerks a little at her words, lifts her head to look at Alex, concerned again. “I…”

“It’s okay,” Alex tells her, cups her face, heart pounding in a different way as Kara leans into it. “I’ll tell you if anything hurts.” If it really hurts, at least, and then mostly because Alex probably won’t be able to hide it. And she knows Kara would never forgive herself, even if Alex doesn’t mind.

“Okay,” Kara says. And then she starts to move.

Her hips don’t move, they’re still flush against Alex’s, but her arral does—an undulating, twisting motion, rubbing against Alex’s inner walls. Alex gasps, bucks, grabs at Kara’s back for something to hold onto. It feels _good_ , waves of pleasure washing over her. Kara hisses, leans into the contact.

“Can you—with your hands?” Kara gasps, and Alex fumbles to rub at the udhivi around Kara’s shoulders, feels them pulse, vibrate around her. Kneads at Kara’s neck, feels Kara panting, the thrill that this is something Alex is doing for her.

Alex had no idea sex would feel like this. She might have kept trying to have it even after the failed experiment with Jason if she’d known, but then—it would have been different with a boy, or with a human girl, and this is better. Not the sex itself, she has no other frame of reference, but that this, her body, is something she can give Kara.

That she can let Kara hold her down, chasing her own orgasm, thrusting in and out somehow, even though she hasn’t pulled the rest of her body off Alex since she pushed inside of her. That she can make her feel good too by touching, trying to soothe all of the udhivi she can reach. And Alex’s hips buck helplessly against the intrusion, she’s sweaty from the struggle, but she’s held firm, _safe_ , pinned beneath Kara’s heavy weight. The only sounds she can hear are their breathing, the rain, the squelch of the arral as it twists inside her own wetness.

Kara’s eyes are closed, she lets out breathy little whines, and Alex runs shaky hands along her cheekbones, her lips, wants to touch all of her she can reach, ground her here in this moment, where she’s so close to Kara. Sharing the same breath, connected, buoyed up together in the storm around them.

And then Kara’s arral bunches up somehow and there’s more pressure, thick, heavy. Kara cries out, and Alex can feel her spurting inside of her this time.

The swelling hurts, but it’s a good hurt, enough pain to tie her here, and that, and feeling Kara come is enough for Alex to come too. Gasping, digging her nails into Kara’s arms, clenching down so hard it hurts more, and that just pushes her higher. They’re both here, and they’re together, and this is where Alex wants to stay.

Eventually, the moment fades, tide rolling back out. When Alex looks up to make sure Kara is okay, that she’s here too, the cilia are slowly drawing back into Kara’s skin, the glow fading with them.

“It worked,” Kara says, voice high in disbelief, and then she laughs, holds up one hand so she can look at her skin, smooth and warm again.

It _worked_. Tears well up behind Alex’s eyes. Kara is still naked on top of her, her arral is still inside Alex, and she’s all mussed hair and flushed, human-looking skin. Kara’s okay. She’s not going to be trapped in the house, or locked up by alien hunters, and Alex can’t stop the tears from falling.

“Are you okay?” Kara asks, alarm on her face. She tries to push up with her arms, pull back, but that _hurts_ , and Alex hisses, grabs at her hip to stop her.

“Sorry!” Kara says. “I’m sorry!”

“I’m fine,” Alex says. “I think it just needs to, um. Stay there for a while.” Swollen and pumping Kara’s cum inside Alex. Shit. She’s going to have to find a morning after pill from the drug store later, just in case, because she’s definitely not on birth control. She probably should have thought about condoms.

“No, I mean... you’re crying,” Kara says. She hesitates, then reaches out to wipe a tear away from Alex’s face, her hand warm against Alex’s cheek. Alex leans into the contact, breathes out, shaky. She shouldn’t be crying. There’s no good reason to be crying over this. She tells Kara anyway.

“I’m relieved,” she says. “I’m just. I’m really happy you’re okay.”

“Me too,” Kara says, smile flickering across her face, like she’s trying to tamp down her excitement but can’t quite manage it. She hesitates, pushes up on one arm a little so she’s no longer chest to chest with Alex, just belly to belly, and she’s still so _close_. “Um. Was it okay for you?”

“It was good,” Alex manages. “I came, so.” Good isn’t the word Alex is looking for, but she can’t find the right one for the relief welling up inside her. They’re bound so closely together, and Alex feels fragile and exposed. Kara is fine, and... still inside her. Now Alex has to think about the fact that they just had sex, and more than that, that it was kind of amazing.

“Yeah,” Kara says, smiling slowly. “Thank you.” She shifts as if she’s going to try to withdraw again but catches herself in time, settling further down onto Alex instead.

“You don’t have to thank me,” Alex says, swiping at the tears on her face, trying for a smile. “We covered this. Protecting you is kind of my job, yknow.”

It’s apparently the wrong thing to say. Kara sits up a little further, shoulders curling, trying to hide with her hair. “Your job,” she says. “Yeah.”

And fuck, that isn’t what Alex meant at all. Only that’s how she’s meant it in the past. Something her parents, and then just her mother, repeated to her ad nauseam.

_Kara’s new to Earth, Alex. You have to protect her._

_Take care of your sister, Alex._

It’s Alex’s job to make sure Kara knows things on Earth, like not using her powers in public, or trying to bathe in water fountains, or walking in on people having sex. But Alex _wants_ to take care of Kara too.

And sex was something Alex had wanted to do, that she’d researched and experimented with, and thought she was fine having with Kara because it would help, and it made sense. And all of those things are, were true, but are missing the big picture.

Alex liked being on her knees in front of Kara, doing something to make her feel good that had nothing in it for Alex, even though she’d sort of hated doing it for Jason, thought the one-sided nature of it was why. She likes this right now, being _close_ to Kara, even though it means she can’t pull away and Kara is like the sun—being too close to her for too long feels like it might burn her up. She likes the feeling of having made Kara undeniably happy right now—or feel good physically at least. She hopes she made her happy too.

“It was great,” she tells Kara, stares at her so that when she looks back again, surprised, Alex can look her in the eye. “I wanted to do it because I wanted to help, but I didn’t know it would feel like that. It wasn’t just the sex, or your arral, or your udhivi, even though I really liked them too,” Alex flushes, admitting it—she is really going to have to do some research into alien sexuality at some point—“it was doing those things with you, Kara. I liked making you feel good. I liked feeling close to you.” Saying these things out loud feels like stripping had earlier, only worse. But Alex thinks Kara needs to hear them.

Kara, on top of her, looks soft and uncertain, but her eyes are shimmering. “That’s why I wanted to turn off the implant,” she says. “Not because I thought anything like this would happen! But I know humans connect through sex. I thought, if I could feel what that felt like, maybe it would help me feel more connected here too. And it did, after everything started hurting less. But I’ve always felt connected to you. This was just… another way of connecting.”

Kara’s expression is raw and open, and the moment feels big enough to drown in, to surround both of them, and Alex wants to sink, wants to _stay_.

“Can I kiss you?” Alex asks, and Kara drops down, hesitant, hopeful, to meet her. Her lips are so soft, tentative on Alex’s, and Alex feels all the tension flooding away from her body in a rush, like she’s floating in the absence of it. She presses back against Kara, wraps her arms around her and pulls her as close as she can.

*

They keep kissing. Kara is warm on top of her, and her weight is still pressing Alex into the bed, and she _likes_ it—it feels like Kara is anchoring her down, like she’s never going to leave. Alex doesn’t want her to leave.

Eventually though, there’s a different sort of movement in her lower body. Kara’s arral pulls free with a squelching sound, and then there’s the uncomfortable sensation of fluid rushing out of her. Alex looks down just in time to see Kara’s arral pull back into her body.

“I’ll get towels,” Kara says, scrambling for the hall closet. Alex stares down at her crotch, red and sore and still slowly leaking blue-tinged fluid into the comforter. Sex is kind of messy. It makes sense, thinking about it, it’s just not what she was expecting. Then again none of this has been what she expected. Mostly in a good way.

“Here!” Kara reappears with an armload of dry towels and a couple of damp wash cloths, and Alex can’t help the laugh that bubbles out of her. Kara looks so earnest, and sincere about her offering, and she’s still completely naked. Without the glowing tendrils, the evidence of something being wrong, it’s just funny, to be walking around the house naked during the day, and charming that she thought about Alex’s comfort before finding clothes for herself. (Looking at Kara naked is nice, too, now that they’ve had sex, that Alex is maybe allowed to stare. It stirs something inside her that she shoves back down, because she’s already kind of sore—this was enough, for today.)

“You know I need to take an actual shower, right?” Alex says. “I’m kind of sweaty—downsides of not having alien powers.”

“Right,” Kara says, smiling, but it fades after a moment.

“Are you okay?” Alex asks, sitting up and paying closer attention. “It did work, right?” She’s not opposed to, well, more, but the thought that Kara might not be okay now, after all of that, is terrifying.

“I’m fine,” Kara says, moving to hand the towels to Alex, and Alex breathes out, trying to slow her heart again. It’s going to take some time to stop jumping to worry, after so much of it.

Kara twists her hands together when they’re empty again. “I just... I still don’t know why this happened. I wasn’t watching porn, or turned on all the time or anything, it just... felt like pressure, building up under my skin. What if this happens again?”

From the bed, Alex reaches out a hand for Kara (she really doesn’t want to find out if alien cum is hard to clean off the floor too), and when Kara moves over Alex touches her hand, smooths her thumb over the back of it. Kara relaxes at her touch, and Alex likes this, likes being able to make Kara feel better by touching her even when she isn’t blue and glowing. She thinks spending the rest of the afternoon watching movies on the couch might be called for, because this definitely counts as a sick day. Maybe they can cuddle. “I’m more than happy to do this again,” she says. “Whether the udhivi come back or not.”

Kara smiles, a little worried, but—happy. “Me too,” she says. Alex thinks she’ll need to get some regular birth control.  
  


**Author's Note:**

> Just as a worldbuilding note, for anyone curious--the sex was not actually necessary to deal with the udhivi, the bath probably would have worked, maybe with some added stroking in there, and Kara jerking off definitely would have worked eventually too. But... y'know. Just as well they didn't know that in this case :) 
> 
> Also, all I want for (belated) Christmas is comments! :D If you liked it, please let me know!


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